The present invention relates to carbon dioxide indicators for use with a resuscitation bag.
The need for, and practice of, endotracheal intubation into the trachea of a patient is well-known. Such intubation is performed when it is found that normal ventilation of the patient's lungs may be impaired. Failure to artificially ventilate an apneic patient rapidly could result in serious brain damage or death.
In general, the endotracheal tube which is used to provide ventilation is a flexible tube which defines an internal respiration lumen so that once the tube has had its distal end placed within the trachea of the patient, a bidirectional breathing path is established through the respiratory lumen. In the case of interruption of the respiratory process, a resuscitator bag can be attached to the proximal end of the endotracheal tube, which end extends external to the patient.
One of the long recognized disadvantages of the use of an endotracheal tube is that an accidental misplacement of the tube into the esophagus can in itself cause death and disability if not quickly detected. In the prior art, a primary means of detecting accidental esophageal intubation has been utilizing a gaseous element detector connected within the air flow path of the respiring patient.
U.S. Pat. Nos. 4,728,499; 4,879,999; and 4,994,117 are examples of prior art devices which utilize a carbon dioxide detector to ensure proper placement of the endotracheal tube. The general concept of detecting the presence of carbon dioxide is a successful safety measure to detect esophageal intubation. Carbon dioxide, a product of metabolism, is normally present in exhaled air in approximately a 5% concentration, but is only minutely present in esophageal gas. Thus, if an approximately 5% concentration of carbon dioxide is detected in air exhaled from the endotracheal tube, the tube is not misplaced in the esophagus. In preferred embodiments of this safety device, a calorimetric carbon dioxide detector is used to enable the personnel responsible for placing the endotracheal tube to have a rapid visual indication of the presence of carbon dioxide.
A resuscitator bag may also be used with a mask placed over a patient's mouth and nose, with the carbon dioxide indicator revealing whether the patient is ventilating at all by exhaling carbon dioxide. Preferably, the indicator turns one color in the presence of carbon dioxide, and then turns back to another when the concentration drops due to the inspiratory breath given to the patient.
FIG. 1 illustrates a prior art resuscitator bag assembly 10 attached to an endotracheal tube 12 inserted into a patient's trachea 14. The assembly includes a resuscitator bag 16 having an inlet port 18 and an outlet port 20. A regulator 22 is attached to the outlet port 20 to provide gases or air from bag 16 through an elbow connector 24 to endotracheal tube 12. An exhaust port 26 connected to regulator 22 provides a path for exhaled gases to be exhausted. An indicator strip 28 is mounted in one end of the regulator 22 to provide an indication of carbon dioxide by changing color. Such a device is described in more detail in U.S. Pat. No. 5,279,289.
FIG. 2 is a cutaway view of one embodiment of a prior art regulator 20 of FIG. 1. When the resuscitator bag 16 is compressed, air or gas is forced along a path indicated by dotted line 30 through a slit at the peak of a duckbill valve 32 to the patient. The forced air or gas causes a gap 34 between the duckbill valve and a tubular lumen 36 to close, blocking off an escape path through exhaust port 26. When air is exhaled by the patient, it follows a path indicated by dotted lines 38 through the regulator, through openings 34 which are pressed open by pushing the duckbill valve 32 lower, and out exhaust port 26.
In this embodiment, the exhaust gases must pass through a barrier filter 40 to reach indicator 28. This can slow the response time of the carbon dioxide indicator. In addition, since the indicator is out of the direct flow path, it will not be cleared by a reduction in carbon dioxide concentration upon forced entry of air to a patient. This is because the carbon dioxide will be caught in the dead space by the indicator. While this is useful for indicating a single exhalation of a patient, it does not allow breath-to-breath determination. The lack of a breath-to-breath indication can give a false reading of proper intubation. In some instances carbon dioxide may be present in a patient's stomach sufficient to cause an initial indication, but not repeated indications. For instance, if a patient recently consumed a few sodas, there may be sufficient carbon dioxide to provide a false indication of proper intubation. Although the CO.sub.2 would decrease over time in this case, the initial false indication would have serious clinical implications. A more detailed description of an apparatus as in FIG. 2 is set forth in U.S. Pat. No. 5,375,592.
U.S. Pat. No. 4,945,918 to Abernathy shows a carbon dioxide indicator strip in a closed-end chamber just beyond an exhaust port for a resuscitator system.
FIG. 3 is a diagram of a prior art carbon dioxide indicator which can be separately inserted into the line between a resuscitator bag and a patient, such as between elbow connector 24 and endotracheal tube 12 of FIG. 1. The assembly of FIG. 3 has a carbon dioxide indicator paper 42 which is viewable through a clear dome 44. Gases can pass through a porous filter 46 and through and around a baffle and indicator support 48. The disadvantage of such an indicator assembly is that it is another piece which must be assembled before treating the patient. At times, it may be time critical to quickly provide air to the patient, and such additional parts to assemble can be a disadvantage.
It would be desirable to have a carbon dioxide indicator which is part of the resuscitator assembly and is located so as to provide breath-to-breath indications.